Method of making electrical contacting elements



Jan. 11, 1949. G. BLAmgER 2,458,552

METHOD OF MAKING ELECTRICAL CONTACTING ELEMENTS Original Filed Dec. 20, 1943 INVIENTOR By 0. a. BLATTNER ATTORNEY Patented Jan. 11, 1949 METHOD OF MAKING ELECTRICAL CONTACTING ELEMENTS David G. Blattner, Mountain Lakes, N. 3., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Original application December 20, 1943, Serial No.

514,943. Divided and this application November 9, 1946, Serial No. 708,855

. amount of the noble metal required for the contact and at the same time prolong the life of the composite wiper.

A still further and more particular object is to set forth a means of manufacturing the composite wiper, having the above advantages, by means of a simple and economically practical process, the steps of which may be followed one after the other at the same place with inappreciable time delays between said steps or may be followed at different places and with considerable time delay between said steps.

In certain types of telephone switching apparatus brushes or wipers may be required to travel over a multiplicity of terminals before arriving at the one with which electrical contact is desired, and when it arrives at the desired terminal it is essential that an intimate, low-resistance contact should be established, particularly when the contact is in a circuit carrying talking currents. One way of obtaining such a contact is to make the terminal and the wiper of a noble metal. This, however, is expensive and furthermore may not be entirely satisfactory because of the fact that the wiper and terminal must not only be made of suitable material, but they must also be held in contact with suitable mechanical pressure and materials suitable from a contact point of view do not in general have good spring characterisitcs. It is therefore desirable in such apparatus to make the wiper of a base metal that is inexpensive and'which has suitable mechanical characteristics and to make the contacting portion thereof of noble metal. Several ways have been proposed for accomplishing this result. One is to plate the contact-carrying portion of the base metal member with noble material. Another method proposed is to insert a plug of noble metal into a hole in a bar of base metal in the conventional manner and after suitable bonding treatment therebetween to roll the composite structure to the desired thickness after satisfactory, but this method is not readily adapted to manufacturing practices. Other methods that have been considered involve riveting or welding a ribbon or bar of contact material to the tip of the base metal member but such constructions also are open to objections from the manufacturing standpoint as well as others. In applicant's invention all difficulties with these prior suggestions are overcome and a further advantage is realized by making it possible to punch the wipers from a strip of material similar to the practice followed heretofore for base metal wipers; but with a strip of noble metal arranged lengthwise thereof in the form of a novel edge lay so that the contacting portion of the wiper is formed from the noble edge lay portion. It is well known that the bond between the base metal and the noble metal of a conventional bimetal edge lay strip is not always satisfactory, and a feature of the applicants invention is therefore to provide a method of manufacture which permits increase in the bonding area and proper disposition of it so as to increase the mechanical reliability and to facilitate manufacture, realization of suitable strentgh, securing of a long life noble metal contact in so far as wear of the Wiper is concerned and reduction to a minimum of the amount of noble metal. required.

The invention has been illustrated in the accompanying drawings in which:

Fig. 1 shows a typical terminal bank and a wiper on a shaft for establishing electrical connections with said terminals;

Fig. 2 shows an enlarged cross-section of the compound noble metal and base metal bars from which the wipers are made;

Fig. 3 shows a sheet rolled out from such a composite bar as shown in Fig. 2 and comprising the noble metal band and the base metal sides with wipers marked as punched out from the sheet; 1

Fig. 4 shows a side view of a wiper made in accordance with my method;

Fig. 5 shows an enlarged side view of a portion of the free end of a wiper;

Fig. 6 shows an enlarged top view of the end shown in Fig. 5; and

Fig. 7 shows an enlarged cross-section of the free end with the noble metal tip engaging a a typical terminal bank which may consist of a semicircular arrangement of terminals 5 arranged in horizontal planes with suitable insulation plates 6 between the layers and suitable end plates 1 and binding screws 8 for holdingthe parts together in a complete terminal bank. A shaft 9 is provided on which a typical wiper assembly I may be mounted and so arranged that on the rotation of the shaft the 'free tip of a wiper will engage the surfaces of succeeding terminals 5 of the group. It is, of course, understood that this is merely a typical illustration of wipers and terminal banks well-known in the art and that my invention may be applied to other types without departing from the spirit thereof.

To manufacture wipers in accordance with my invention, a noble metal bar or slug I5 is provided as shown in Fig. 2 of a trapezoidal crosssection with the two opposite sides It and I1 parallel and the two opposite sides [8 and I9 slanted towards each other from the base side l1 to the top side l6. Adjacent to the side I8 is placed the base metal bar 22 of the same thickness as the distance between the sides i6 and ll of the noble metal slug and a similar bar 23 is placed adjacent to the side I9. An alternative arrangement would be to provide in place of bars 22 and 23 a single bar with a suitable slot therein to accommodate the slug i5. It is also to be understood that my method of manufacture includes such a procedure as may comprise the use of only one bar such as 22 or 23 with the noble metal slug i5. It may be advisable in some instances to so modify the composite bar shown in Fig. 2. The preferred method is as shown but is not intended to exclude from the scope of the invention such obvious rearrangements as mentioned above. The bars 22, I5 and 23 are then welded or otherwise bonded together by methods well known in the art and the composite structure is then rolled out lengthwise so as to form a strip of the proper thickness and flexibility required for wipers. Such a strip is illustrated by numeral 26 in Fig. 3 and it should be noted that the noble metal bar I5 is shown with its side l6 towards the top while the bottom side I! is shown in dotted lines. By rolling out this compound bar in this manner the transverse dimension of the sides l6 and I! remain practically the same as in the bar before it is rolled out. Therefore, in the rolled-out strip the slanting surfaces l8 and is will assume angles toward the top surface which are considerably less than the angles these sides had in the original bar. The original angle 29, for example, is shown on the compound bar in Fig. 2, and the corresponding resulting angle 30 is shown in the enlarged cross-section in Fig. 7. It is obvious that this slanting bond produces bonding surfaces considerably larger than would be produced had the cross-section of the bar I5 been in the shape of a parallelogram in which case the bonding surfaces in the rolled out strip would have an area corresponding only to the thickness of the rolled out strip. To illustrate the increase in bonding surface area and referring particularly to Fig. 7, the length 3| of the bonding surface marked 32 may be, for example, .05 inch while the thickness 33 of the wipers may be only .01 inch, thus making the slanting bonding surface 32 five times as wide as a bonding surface if run perpendicularly across the' wiper with the resulting effect that the bond would be at least five times as strong as could be obtained with the conventional type of edge lay bond. It is not to be assumed, however, that the scope of.the invention is limited to producing any particular magnification of bondin surface.

From this strip 26, Fig. 3, may be punched out wipers of the desired formation in pairs such as the pair 34, each wiper being a separate piece but the wipers of a pair having their tips located end to end in the noble metal area so that each wiper would contain a noble metal tip 35 bonded to the base metal shank in the manner described. It would also be satisfactory to slit the sheet lengthwise through the middle of the noble metal strips I6 and punch out the wipers singly instead of in pairs if preferred. ,In either case the processed strip permits manufacture of noble metal-tipped wipers in quantity and therefore advances the art from a manufacturing point of view. After the wipers 34 have been punched out they are formed to desired shape illustrated by the side view, Fig. 4, with the tips 39 on opposite sides of the tip bent slightly upward. The bending of the free (tip) end of the wiper downwardly is accurately gauged so that when the wipers are assembled on the shaft and permitted to ride or come in contact with succeeding terminals of the bank shown in Fig. 1 the longitudinal central axis of the bonding surface 32 of wipers made by means of this invention lies substantially parallel with the upper surface 42 of the terminal 43. Thus it will be seen that not only is a strong bond provided but also that as the noble metal tip wears from use, it wears in such a manner as to consume practically the whole noble metal tip before the base metal is reached and the wiper has to be discarded. This is readily understood from examination of Fig. '7. It should be noted in Fig. 5 that this bonding surface of the wiper lies entirely in the area comprising the free end including the tips 39 so that the bonding surface is of a considerably larger area than it would be if extended across the narrower portion of the wiper. It should be further noticed that due to the fact that the bonding surface 32 lies parallel with the terminal surface 42 the pressure of the wiper against the terminal surface is exerted at substantially right angles to the bonding surface. This gives a tension effect at the bondv whereas with a conventional edge lay bond the bond surface would be substantially parallel with the direction of the forces and would put the bond in sheer stress, an inherently weaker construction.

It will therefore be seen that with the location and arrangement of the bond between the noble metal tip and the base metal shank in this manner a rugged wiper is obtained having a small amount of noble metal and a long life expectancy as compared with other noble metal wipers previously proposed.

There are four main steps to my process of manufacture; namely, forming the composite bar as exemplified by Fig. 2, rolling this bar into a thin flexible sheet of desired thickness, stamping or punching wiper arms from said sheet as shown in Fig. 3 and lastly subjecting these wiper arms to suitable bending and forming operations whereby the desired shape is realized as shown in Figs. 4, 5 and 7. It is possible and in some instances economically more feasible to perform eachof the separate main steps of the process at different places or geographical locations and with considerable time delay between steps and this outlook on the prospective manner of employing the invention is contemplated by my appended claims as is any such process carried on without such time delays and at the same place or geographical location. 1

I have mentioned a few obvious modifications or rearrangements of my invention to show that such, as well as others which will be suggested by the above disclosure, are contemplated as being within the scope of my invention and I append the following claims which alone define the scope thereof.

What is claimed is:

1. The method of manufacturing sheets of composite material from which bank terminal wipers having a noble metal contacting tip and a base metal shank may be punched comprising assembling a noble metal bar of a trapezoidal crosssection with a base metal bar located against at least one of the slanting sides of said noble metal bar, bonding said bars together and rolling said composite bar lengthwise until a thin flexible sheet is obtained wherein the bonding surface between said noble metal and said base metal is at an acute angle with the plane of said sheet.

2. The method of manufacturing sheets of composite material from which bank terminal wipers having a noble metal contacting tip and a base metal shank may be punched comprising assembling a noble metal bar of a trapezoidal crosssection with a base metal bar located against each of the slanting sides of said noble metal bar, bonding said bars together at the slanting sides and rolling said composite bar so that the original relation between the widths of upper and lower parallel sides of the noble metal bar is substantially retained and until a thin flexible sheet is obtained wherein the bonding surfaces between said noble metal and said base metal are at acute angles with the plane of said sheet.

3. The method of manufacturing wipers for cooperation with bank terminals comprising assembling a noble metal bar of a trapezoidal crosssection with a base metal bar located against at least one slanting side of said noble metal bar, bonding said pars together, rolling said composite bar until a thin flexible sheet is obtained wherein the bonding surface between said noble metal and said base metal is at an acute angle with the plane of said sheet, punching out wipers from said sheet with the contact tips of said wipers located in the noble metal area of said sheet and bending each wiper so that the bonding surface between the noble metal contact tip and the base metal shank will be located substantially parallel with the terminal surface over which it will travel.

4. The method of manufacturing wipers for cooperation with bank terminals comprising assembling a noble metal bar of a trapezoidal crosssection with a base metal bar located against each slanting side of said noble metal bar, bonding said bars to ether, rolling said composite bar lengthwise until a thin flat flexible sheet is obtained wherein the bonding surfaces between said noble metal and said base metal are at acute angles with the plane of said sheet, punching out wipers from said sheet with the contact tips of said wipers located in the noble metal area of said sheet and bending each wiper so that the bonding surface between the noble metal contact tip and the base metal shank will be located substantially parallel with the terminal surfaces over which it will travel.

5. The method of manufacturing wipers for cooperation with bank terminals comprising assembling a noble metal bar of a trapezoidal crosssection with a base metal bar located against each slanting side of said noble metal bar, bonding said bars together, rolling said composite bar lengthwise until a thin flat flexible sheet is obtained wherein the bonding surfaces between said noble metal and said base metal are at acute angles with the plane of said sheet, punching out wipers from said sheet in pairs with the contact tips of each pair located with their ends adjacent in the noble metal area of said sheet and bending each wiper so that the bonding surface between the noble metal contact tip and the base metal shank will be located substantially parallel with the terminal surfaces over which it will travel.

6. The method of manufacturing wipers for cooperation with bank terminals comprising assembling a noble metal bar -of a trapezoidal crosssection with a base metal bar located against each of the slanting sides of said noble metal bar, bonding said bars together at the slanting sides, rolling said composite bar so that the original relation between the widths of upper and lower parallel sides of the noble metal bar is substantially retained and until a thin flexible sheet is obtained wherein the bonding surfaces between said noble metal and said base metal are at acute angles with the plane of said sheet, punching out wipers from said sheet in pairs with the contact tips of each pair located with adjacent ends in the noble metal area and with the longitudinal axis running through each pair located substantially perpendicular to the noble metal bar, and bending each wiper so that the bonding surface between the noble metal contact tip and. the base metal will be located substantially parallel with the terminal surfaces over which the wiper will travel.

7. The method of manufacturing wipers for cooperation with bank terminals comprising assembling a noble metal bar of a trapezoidal crosssection with a base metal bar located against each of the slanting sides of said noble metal bar, bonding said bars together at the slanting sides, rolling said composite bar so that the original relation between the widths of upper and lower parallel sides of the noble metal bar is substantially retained and until a thin flexible sheet is obtained wherein the bonding surfaces between said noble metal and said base metal are at acute angles with the plane of said sheet, punching out wipers from said sheet in pairs with the contact tips of each pair located with their ends connected to each other end to end in the noble metal area and with the. longitudinal axis running through each pair located perpendicular to the noble metal bar, and

severing the connected ends of said wipers and bending each wiper so that the bonding surface between the noble metal contact tip and the base metal will be located substantially parallel with the terminal surfaces over which the wiper will travel.

DAVID G. BLATTNER.

REFERENCES crran' The following references are of record in the file of this patent:

UNITED STATES PATENTS 

